The present invention is directed to the field of storage rack systems. More particularly, the present invention is directed to a push back type of storage rack system for storing a plurality of loads in which multiple loads may be stored in a single storage lane.
Push back storage racks normally comprise an assembly of shelves and vertical uprights for supporting loads placed on tracks or other base members in one or more storage lanes. Each storage lane has one loading position capable of storing one load. One or more vertically spaced push back carts are positioned in the loading position. Each cart is capable of receiving one load, being pushed toward the back of the lane by the next load, and sliding over the top of one another when unloaded. Such systems normally have their tracks in each lane tilted toward the loading position so that the force of gravity causes the next cart in line to return to the loading position when a load occupying the position is removed.
When adding a load to a particular lane, the operator pushes the added load against a previously stored load occupying the lane's loading position. This forces the cart under the previously stored load further up the lane and out of the loading position, thereby making room for the load being added. If additional carts are in the loading position, the operator then positions the load on the next available cart. If all the carts have been pushed out of the loading position, the added load fills the lane to capacity, and the operator places the added load directly onto the tracks or base member of the lane itself.
Previous push back storage systems have also included designs which permit unloaded carts to automatically slide into the loading position of their respective storage lanes to receive loads. Most designs allow the empty carts to simultaneously occupy the same loading position by incorporating either a nesting or telescoping cart arrangement.
In previous nesting designs, higher level carts retract or nest within the horizontal dimensions of each next lower level cart. Such designs have been limited in both the number of carts that can be included in a single system and in the relative strength of each cart since the designs typically require the use of a single pair of track members and since the required horizontal clearance for successive carts prevents the inclusion of structural cross members. Due to the resulting limitations on the amounts of available space in such designs, these characteristics have also severely limited the number of carts that can be used and thus the number of loads that can be stored in a single lane. Additionally, smaller and weaker components may be used which substantially reduce the load-bearing capabilities of the system. In addition to substantially limiting the system's load-bearing capacity, smaller components, such as cart wheels, also tend to increase the amount of external force necessary to operate such systems. This ultimately leads to the need for more steeply sloped track inclines, which are undesirable, and normally increases the amount of wear and potential damage to the system, loading equipment, and stored loads.
In previous telescoping designs, individual carts have been vertically spaced so that each higher level cart merely slides over the top of the next adjacent lower level cart. Previous telescoping designs have been severely limited in the number of carts that can be incorporated in a single lane due to the vertical space needed to include a rigid support piece across the width of each cart. Such cross pieces tend to make the additional vertical height required for each cart too great to incorporate many carts into a single lane. In contrast, eliminating such pieces tends to severely reduce the load capacity of each individual cart.
Previous telescoping designs have also been limited by the fact that most use only a single pair of track members with one or more support surfaces upon which the wheels of the various carts ride. As with nesting designs, this characteristic of most telescoping designs has severely limited the number of carts and thus the number of loads which can be included in a single lane, while posing the same problems of wear, potential damage to the system, equipment, and loads. In the few instances where multiple pairs of tracks have been incorporated, some portions of the various support surfaces have been left unused. As a result, both space and load-bearing capacities have been wasted in such previous systems, reducing their cost-effectiveness and versatility.
In some previous designs, push plates have been positioned at the trailing edge of the lowest or last-loaded cart to assure that an operator maintains proper pallet clearance during loading and to indicate, when it is not visible to the operator, that a particular lane is filled to capacity. It has been observed from time to time that pallets on which loads are stored drag against an adjacent surface of the push plate, causing damage to the pallets during loading and unloading.
Many of the previous designs of push back rack systems have also been plagued by the problem of outward bowing of the beam adjacent each lane's loading position. The problem is associated with the repeated forces exerted by a system's carts as they automatically return to their respective loading positions. As each cart repeatedly returns to this position, stopping forces are exerted upon the adjacent beam member which, over time, tends to bend or warp outwardly and away from the storage lane in which it is mounted This is an additional problem which previous push back storage systems have yet been unsuccessful in resolving.